For motor vehicles, such as, for example, cars, trucks and buses, a fuel cost represents a significant expense for the owner or user of the vehicle. For a haulage company, for example, apart from the cost of procurement of the vehicle, the main items of expenditure for the running of a vehicle are constituted by pay to the driver of the vehicle, costs of repairs and maintenance, and fuel for propulsion of the vehicle. The fuel cost can here have a very large impact on profitability for the haulage company. Hence a number of different systems have been developed in order to reduce fuel consumption, such as, for example, fuel-efficient engines and fuel-saving cruise control devices.
FIG. 1 shows in schematic representation a drive train in a vehicle 100. The drive train comprises an internal combustion engine 101, which is connected in a conventional manner, via an output shaft 102 from the internal combustion engine 101, usually via a flywheel, to an input shaft 109 of a gearbox 103 by means of a clutch 106. The clutch 106 can be constituted, for example, by an automatically controlled clutch, and is controlled by the control system of the vehicle via a control unit 700 (FIG. 7). The control unit 700 can also control the gearbox 103.
The gearbox 103 is here illustrated schematically as a unit. The gearbox 103 can also, however, physically consist of a plurality of interacting gearboxes, for example of a range gearbox, a main gearbox and a split gearbox, which are arranged along the drive train of the vehicle. The gearbox can comprise a suitable number of gear positions. In contemporary gearboxes for heavy duty vehicles, twelve forward gears, two reverse gears and a neutral gear position are usually found. If the gearbox 103 physically consists of a plurality of part gearboxes according to the above, these twelve forward gears are distributed amongst two gears in the range gearbox, three gears in the main gearbox and two gears in the split gearbox, which together constitute twelve gear positions (2×3×2=12). The vehicle 100 further comprises drive shafts 104, 105, which are connected to the drive wheels 110, 111 of the vehicle and which are driven by an output shaft 107 from the gearbox 103 via an axle gearing 108, such as, for example, a conventional differential.
The vehicle 100 further comprises a variety of different braking systems, such as a conventional service braking system, which can comprise, for example, brake disks with associated brake linings (not shown) arranged next to each wheel. The engine 101 can be controlled on the basis of instructions from a cruise control, in order to maintain a constant actual vehicle speed and/or vary the actual vehicle speed so that a fuel consumption which is optimized within reasonable speed limits is obtained. The engine 101 can also be controlled by a driver of the vehicle.